Although I don't have much experience, GDAX offers near instant updates to its trading portal. In addition, it offers candle stick charts down to 1-minute intervals. I've also had good experience with crymptocompare API. I use it in the form of the CryptoFinance app for google sheets. By using the command =GOOGLEFINANCE("BTCUSD") in a cell, it will fetch the updated price for any coin that you can see on cryptocompare.
This is a great way to keep track of coin value. I tried using and I am very pleased about this. Look forward to receiving more of your sharing on how to track trading volatility fluctuations in 24h of different coin to facilitate tradecoin. You can share to everyone who supports you.
I also used it and I felt it was not working well, maybe I did it incorrectly at some point. If you are successful then you can help me do this because I think it really helps a trader like me in this market. Look forward to receiving your support.